Moka Espresso?

At the end of this Wikipedia article on Moka pots, in the 'Moka coffee vs. espresso coffee' section, there are references to an accepted standard for producing espresso. The standard says true espresso must be drawn at 9 bars (atmospheres) of pressure. However, this cannot be verified via any of Wikipedia's citations – none of the listed reference sites demonstrate these standards at this time. What does your experience tell you? When it comes to pressure, is bigger better, or do things really get crema-y somewhere in between?